Stealth technology is getting a makeover with radar-absorbing nanoparticles. On this ultra-small scale, electromagnetic stealth materials offer dramatically enhanced microwave- and millimeter-wave attenuation.
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Shrinking technology to the nanoscale increases specific surface areas enormously and provides a high density of dangling bonds and unsaturated coordination sites.
These features amplify interfacial polarization and enable multiple internal reflections, converting more electromagnetic energy into heat.2
These properties make nanocomposites especially attractive for weight-sensitive and space-constrained applications, from aircraft skins and naval stealth coatings to EMI-shielded enclosures and anechoic chambers.1,2
Physics of Radar Attenuation at the Nanoscale
Radar absorption lies at the heart of stealth technology. Systems detect objects with radar by transmitting pulses of electromagnetic energy and measuring the time delay and intensity of the returned echo.
R is the distance between the radar and the target, c the speed of light, and t the time for the pulse to make a round-trip from emission to its returned detection.3-4
The key parameter governing detectability is the radar cross section (RCS), defined by the ratio of scattered to incident field intensities (σ = |Es|2/|Et|2), which depends on an object’s size, shape, and material reflectivity.4
Radar‑absorbing nanoparticles reduce detectability via two key mechanisms: Electromagnetic losses (dielectric, resistive, and magnetic) that dissipate wave energy as heat, and multiple internal reflections that extend the wave’s path and increase attenuation.
These processes are determined by the material’s complex permittivity (εr) and permeability (μr), the incidence angle θ, and the coating thickness d. In transmission‑line theory, the reflection loss RL (in dB) can be expressed as:
Z0 is ~377 Ω, and is the impedance of free space.
Maximum absorption occurs when the impedance of the absorber closely matches free space. Nanoparticles, with their tailored electromagnetic properties and quantum effects, enable this across a wide frequency range, harnessing high surface area, quantum effects, and tailored dielectric/magnetic properties to achieve broadband stealth from the micro- to the millimeter‑wave regimes.4
Structural Impacts on Absorption
The geometry, composition, and internal architecture of radar‑absorbing nanoparticles can dramatically influence performance.
For example, isotropic La0.8Ba0.2MnO3 nanocrystals of roughly 80 nm diameter achieve a reflection loss (RL) peak of 13 dB at 6.7 GHz and maintain over 10 dB of absorption bandwidth spanning 1.8 GHz when applied as a 2.6 mm coating, with dielectric loss dominating the attenuation.5
Improving crystallinity, such as in BaFe12O19 nanoparticles synthesized via cyclic microwave irradiation, shifts the RL minima to higher frequencies and deepens them dramatically (from -4.21 to -53.69 dB) across the Ku‑band (12-18 GHz), underscoring how morphology tunes absorption.6
Core-shell approaches further broaden and deepen absorption by combining magnetic and dielectric constituents: Ni-P shells on BaNi0.4Ti0.4Fe11.2O19 cores yield -28.7 dB RL in the 12.4-18 GHz range, and annealing at 400 °C expands the >12 dB bandwidth from 1.5 to 4.0 GHz. Whereas TiO2 shells on MnFe2O4 cores enhance both dielectric and magnetic losses, surpassing uncoated particles in the two to 10 GHz band.7
At the extreme nanoscale, encapsulating Er2O3 in carbon nanotube cavities changed its quantum properties, introducing discrete energy levels and stronger Er3+ magnetic dipole moments. This boosted RL from -21.6 dB to -27.96 dB at around 10 GHz and widened the >5 dB absorption window from 3.50 to 4.65 GHz at a fixed two-millimeter thickness, with thickness modulation further tuning peak frequencies.2, 7
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Recent Advances
In a recent study, Wang et al. produced bimetallic Co/Fe nitrilotriacetic acid chelate nanowires via hydrothermal self‑polymerization, varying the Co-to-Fe atomic ratios.8 These nanowire precursors were then calcined to form CoxFey@C nanocomposite fibers.
Notably, the fiber with an equal Co/Fe ratio (1:1) demonstrated exceptional microwave absorption, achieving an impressive minimum reflection loss of -117.8 dB and an effective absorption bandwidth of 12.6 GHz (5.4-18 GHz) at the same thickness. Additionally, its radar cross-section stayed below -10 dBm2 across incident angles from - 60 ° to 60 °, providing nearly full‑angle stealth performance.8
A further study by Wei et al. involved the design of single‑ and double‑layer wave‑absorbing coatings by embedding doped barium ferrite and helical carbon nanotube composites in an epoxy resin matrix.9
The scientists fine‑tuned the coatings’ composition and thickness using an adaptive genetic algorithm linked with simulation tools. The resultant absorbers had a porous, reticular architecture with abundant microvoids and an optimized conduction network.
The optimized coating achieved peak absorptivity, maximal RCS reduction, minimal input reflection coefficient, and a highly uniform scattering pattern, delivering outstanding microwave absorption with a reflection loss as low as -17.22 dB at 16.66 GHz and an absorption bandwidth reaching 9.16 GHz.9
And even more recently, Choudhury et al. investigated the EMI‑shielding performance of thermoplastic elastomer blends composed of EPDM (ethylene‑propylene‑diene rubber) and LLDPE (linear low‑density polyethylene) loaded with conductive Vulcan carbon black via a conventional melt‑blending process. Their extensive experiments showed that melt‑blended EPDM/LLDPE/VCB composites (ELV) provide a flexible, lightweight, durable, and cost‑effective EMI‑shielding solution.10
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Emerging Applications
Stealth Technology
Radar‑absorbing nanocoatings complement geometric stealth by absorbing radar energy. They can reduce aircraft RCS by preventing incident radio waves from bouncing directly back to the radar receiver.
Where traditional stealth relies on airframe contouring and frame restructuring to scatter microwaves away from the source, nanocomposite coatings instead absorb and dissipate incident pulses through dielectric, resistive, and magnetic losses, as well as via multiple internal reflections.1, 4
By diffusing the reflected energy rather than producing a single specular echo, these coatings can mimic the low-RCS signature of small clutter on a much larger metal surface. This enables fighters built from ordinary metals to achieve stealth levels that have previously only been possible with specialized alloys or carbon‑fiber airframes.
When combined with conventional shape‑based methods, radar‑absorbing nanoparticles allow modern combat aircraft and naval vessels to approach and penetrate defended airspace with a minimal probability of detection.4
EMI Shielding
Core-shell nanocomposites like collagen fiber/Fe3O4/polypyrrole (CF/Fe3O4) deliver high-performance EMI shielding by integrating magnetic, dielectric, and conductive losses in a layered core-shell structure.11
The hierarchically porous CF scaffold induces multiple reflections and extended propagation paths for incident waves, dramatically enhancing attenuation across 2-18 GHz. As a result, these nanocomposites achieve exceptional shielding effectiveness of ~72 dB with an absorption contribution of ~85.8 % and a specific SE of 360 dB cm2 g-1, offering a lightweight, thin‐profile solution to suppress EMI without secondary reflections.11
Conclusion and Future Perspective
Radar‑absorbing nanoparticles perform best in 3D architectures that combine impedance matching with high loss and interfacial scattering. These structures create multiple internal reflections, maximizing attenuation.
To scale this tech up, focus is shifting towards methods such as chemical vapor deposition, magnetron sputtering, atomic layer deposition, or wet‑chemistry routes to produce core-shell, block, or foam architectures, which can overcome the uneven interfaces and dispersion challenges inherent in multilayer designs.
Bridging this lab success with commercial production will depend on close collaboration between researchers and industry. Bringing down costs without compromising performance is essential if these materials are to power the next generation of stealth technology.
References and Further Studies
- Bera, P.; Lakshmi, R.; Barshilia, H. C., An Overview of Radar-Absorbing Materials and Coatings for Stealth Application. SCIENCE AND CULTURE 2025.
- Wang, Y.; Li, T.; Zhao, L.; Hu, Z.; Gu, Y., Research Progress on Nanostructured Radar Absorbing Materials. Energy and Power Engineering 2011, 3, 580-584.
- Gu, W. et al. A Lightweight, Elastic, and Thermally Insulating Stealth Foam with High Infrared‐Radar Compatibility. Advanced Science 2022, 9, 2204165.
- Kim, S.-H., et al. Carbon-Based Radar Absorbing Materials toward Stealth Technologies. Advanced Science 2023, 10, 2303104.
- Zhou, K.-S. , Microwave Absorbing Properties of La0. 8ba0. 2mno3 Nano-Particles. Transactions of Nonferrous Metals Society of China 2007, 17, 947-950.
- Sharma, R.; Agarwala, R.; Agarwala, V., Development of Radar Absorbing Nano Crystals by Microwave Irradiation. Materials Letters 2008, 62, 2233-2236.
- Sharma, R.; Agarwala, R.; Agarwala, V., Development of Electroless (Ni-P)/Bani0. 4ti0. 4fe11. 2o19 Nanocomposite Powder for Enhanced Microwave Absorption. Journal of alloys and compounds 2009, 467, 357-365.
- Wang, B., et al. Facile Synthesis of Coxfey@ C Nanocomposite Fibers Derived from Pyrolysis of Cobalt/Iron Chelate Nanowires for Strong Broadband Electromagnetic Wave Absorption. Chemical Engineering Journal 2023, 465, 142803.
- Wei, S. et al., Constructing and Optimizing Epoxy Resin-Based Carbon Nanotube/Barium Ferrite Microwave Absorbing Coating System. Materials Research Bulletin 2024, 179, 112928.
- Choudhury, S. N. et al. Development of Conductive Thermoplastic Elastomer Blend Nanocomposites for Enhanced Electromagnetic Interference Shielding in Modern Electronics. Next Nanotechnology 2025, 7, 100193.
- Liu, C.; Liao, X., Collagen Fiber/Fe3o4/Polypyrrole Nanocomposites for Absorption-Type Electromagnetic Interference Shielding and Radar Stealth. ACS Applied Nano Materials 2020, 3, 11906-11915.
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